Plots in the Case of One Adsorbed Species

The faradaic admittance of reactions (116) and (117) is described by Eq. (135). Analysis of the complex plane plots in such a case was presented by Cao. Bai and Conway presented three-dimensional plots for such a reaction. Two general cases should be considered, depending on the sign of the parameter B  

It changes from R l at very high frequencies to R d - B /C at very low frequencies. The faradaic impedance is described as 

The limit of faradaic impedance at infinite frequency is also called the transfer impedance, R, while the limit at zero frequency is called the polarization resistance, Rp  

In our case / = / + Ra iB / C — IBI) and / ,= R Equation (140) represents a series connection of the charge-transfer resistance with a parallel connection of the resistance / and pseudocapacitance Cfl. The complete equivalent circuit in this case is shown in Fig. 21. The observed complex plane plots depend on the sign of the denominator of Ra. la. C-R B 0 

In this case all the elements are positive and the faradaic impedance represents one semicircle on the complex plane plots (see Fig. 22). When Cj, the total impedance represents two semicircles (Fig. 22). When A B /C the faradaic impedance is equal to R. . The complex plane plots are analogous to those shown in Fig. 4 and represent one capacitive semicircle. 

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